The claimEvidence A · guideline-tier
5-10 mg melatonin helps you sleep
The evidence
A physiological dose of 0.3 mg works as well; 5-10 mg overloads the receptors, bringing next-day grogginess and a disrupted body clock.
Why the claim spreads
Sold over-the-counter in big doses in the US, feeding the 'more = stronger' intuition; most people never learn the effective dose is far smaller.
The mechanism, in brief
Melatonin is not a sleeping pill that knocks you out. It is a message: it is dark now, time to get ready for sleep. About two hours before your usual bedtime, a pea-sized gland deep in the brain, the pineal gland, starts releasing it into the blood.
Sources (4)
- Brzezinski, A., et al. (2005). Effects of exogenous melatonin on sleep: a meta-analysis. Sleep Medicine Reviews, 9(1), 41–50. 17 studies, 284 subjects: melatonin reduced sleep onset latency by 4.0 min (95% CI 2.5-5.4), increased sleep efficiency by 2.2% (0.2-4.2) and total sleep by 12.8 min (2.9-22.8); in the 15 studies of healthy people or people with insomnia only: 3.9 min, 3.1% and 13.7 min (abstract, PMID 15649737).
- Cajochen, C., Kräuchi, K., & Wirz-Justice, A. (2003). Role of melatonin in the regulation of human circadian rhythms and sleep. Journal of Neuroendocrinology, 15(4), 432-437. Review of endogenous melatonin as the internal signal of biological night: secretion is driven by the suprachiasmatic nucleus and suppressed by light, and the hormone feeds back on the SCN through MT1 and MT2 receptors, with sleep-promoting effects that track its thermoregulatory action rather than a hypnotic one.
- Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232-1237. In a controlled in-laboratory crossover, reading from a light-emitting eReader for four hours before bed across five consecutive evenings suppressed evening melatonin, delayed circadian timing and sleep onset, reduced REM sleep, and left participants less alert the next morning, compared with reading a printed book. Full text: 12 healthy young adults (6 women), 14-day inpatient randomized crossover; about 4 h of reading before bedtime in otherwise very dim room light on 5 consecutive evenings per condition (the eReader held at 30-50 photopic lux in the angle of gaze; the printed book reflected about 0.9 lux). On night 5 the eReader suppressed evening melatonin by 55.12 ± 20.12% (print book: none); dim-light melatonin onset was more than 1.5 h later (22:31 vs 21:01); sleep latency was nearly 10 min longer (25.65 vs 15.75 min); total sleep time and sleep efficiency did not differ (full text, PMC4313820; abstract, PMID 25535358).
- Lelak, K., Vohra, V., Neuman, M. I., Toce, M. S., & Sethuraman, U. (2022). Pediatric melatonin ingestions — United States, 2012–2021. MMWR Morbidity and Mortality Weekly Report, 71(22), 725–729. National Poison Data System 2012-2021, ages 19 and under: 260,435 pediatric melatonin ingestions, the annual number up 530%; 4.9% of all pediatric ingestions reported in 2021 vs 0.6% in 2012; hospitalizations and serious outcomes rose, mainly from unintentional ingestions in children aged 5 or under; 5 children needed mechanical ventilation and 2 died. US over-the-counter melatonin sales rose from $285 million (2016) to $821 million (2020) (abstract, PMID 35653284).